diff --git a/dom/xhr/XMLHttpRequestMainThread.cpp b/dom/xhr/XMLHttpRequestMainThread.cpp
index aa97f8b0b51e..ec4212aa501e 100644
--- a/dom/xhr/XMLHttpRequestMainThread.cpp
+++ b/dom/xhr/XMLHttpRequestMainThread.cpp
@@ -2858,7 +2858,7 @@ nsresult XMLHttpRequestMainThread::SendInternal(const BodyExtractorBase* aBody,
 
   mIsMappedArrayBuffer = false;
   if (mResponseType == XMLHttpRequestResponseType::Arraybuffer &&
-      IsMappedArrayBufferEnabled()) {
+      StaticPrefs::dom_mapped_arraybuffer_enabled()) {
     nsCOMPtr<nsIURI> uri;
     nsAutoCString scheme;
 
@@ -2954,20 +2954,6 @@ nsresult XMLHttpRequestMainThread::SendInternal(const BodyExtractorBase* aBody,
   return rv;
 }
 
-/* static */
-bool XMLHttpRequestMainThread::IsMappedArrayBufferEnabled() {
-  static bool sMappedArrayBufferAdded = false;
-  static bool sIsMappedArrayBufferEnabled;
-
-  if (!sMappedArrayBufferAdded) {
-    Preferences::AddBoolVarCache(&sIsMappedArrayBufferEnabled,
-                                 "dom.mapped_arraybuffer.enabled", true);
-    sMappedArrayBufferAdded = true;
-  }
-
-  return sIsMappedArrayBufferEnabled;
-}
-
 // http://dvcs.w3.org/hg/xhr/raw-file/tip/Overview.html#dom-xmlhttprequest-setrequestheader
 void XMLHttpRequestMainThread::SetRequestHeader(const nsACString& aName,
                                                 const nsACString& aValue,
diff --git a/dom/xhr/XMLHttpRequestMainThread.h b/dom/xhr/XMLHttpRequestMainThread.h
index 2a3f6ae9250c..0b6581f7b466 100644
--- a/dom/xhr/XMLHttpRequestMainThread.h
+++ b/dom/xhr/XMLHttpRequestMainThread.h
@@ -300,10 +300,6 @@ class XMLHttpRequestMainThread final : public XMLHttpRequest,
 
   void UnsuppressEventHandlingAndResume();
 
-  // Check pref "dom.mapped_arraybuffer.enabled" to make sure ArrayBuffer is
-  // supported.
-  static bool IsMappedArrayBufferEnabled();
-
   void MaybeLowerChannelPriority();
 
  public:
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index 5c75336efea3..2dacd59b8d48 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -1628,6 +1628,12 @@
   value: false
   mirror: always
 
+# Enable mapped array buffer by default.
+- name: dom.mapped_arraybuffer.enabled
+  type: bool
+  value: true
+  mirror: always
+
 # This pref is used to enable/disable the `document.autoplayPolicy` API which
 # returns a enum string which presents current autoplay policy and can change
 # overtime based on user session activity.
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 80373b3783a3..c8066ebd751f 100755
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -5035,9 +5035,6 @@ pref("captivedetect.maxWaitingTime", 5000);
 pref("captivedetect.pollingTime", 3000);
 pref("captivedetect.maxRetryCount", 5);
 
-// Enable mapped array buffer by default.
-pref("dom.mapped_arraybuffer.enabled", true);
-
 // The tables used for Safebrowsing phishing and malware checks
 pref("urlclassifier.malwareTable", "goog-malware-proto,goog-unwanted-proto,moztest-harmful-simple,moztest-malware-simple,moztest-unwanted-simple");
 #ifdef MOZILLA_OFFICIAL